The giant wildfire burning at the edge of Yosemite National Park has unleashed a smoky haze that has worsened air quality more than 100 miles away in Nevada.

The plume from the Rim Fire in California triggered emergency warnings in the Reno and Carson City area.

Schoolchildren were kept inside for the second time in a week, people went to hospitals complaining of eye and throat irritation and officials urged people to avoid all physical activity outdoors.

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A smoky haze from a huge California wildfire burning more than 150 miles away hangs over Virginia Street in Reno, Nevada

The wildfire threatening Yosemite National Park is still burning its way into the huge US tourist attraction and spreading unhealthy air all the way to Nevada (pictured on August 28)

'It's five hours away,' said 22-year-old bartender Renee Dishman in disbelief after learning that the source of the haze was more than 150 miles away. 'I can't run. I can't breathe. It makes me sneeze.'

The Rim Fire, so far, has burned through 293 square miles, destroyed more than 100 structures, including 85 tent cabins at a camp run by the city of Berkeley, and threatened water supplies, hydroelectric power and giant sequoias.

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This morning, authorities said the blaze was 23 per cent contained, with crews aided by higher humidity continuing to make progress against it overnight.

In Nevada, evidence of the Rim Fire is in the smoke-filled sky. The air quality index briefly surpassed the rare 'hazardous' level east of Lake Tahoe before improving slightly.

It hovered around the next-most serious stage of 'very unhealthy' for all populations in the Reno-Sparks area 30 miles north.

Dennis Fry, a Reno auto body specialist for nearly 30 years, remembered smoke this thick when he worked on a logging crew and helped fight fires in Oregon during the 1970s.

Most of the Sierra's eastern front from south of Carson City to north of Lake Tahoe has been under an air quality alert for nearly a week (Reno, Nevada pictured)

Angel City fire fighters Cody Stephens, left, and Kevin Brown, center, wait as helicopter dumps water on hot spots battling the Rim Fire in the Stanislaus National Forest along Highway 120 near Yosemite

'But never in Reno, not this bad,' he said. 'You could actually see the smoke inside my body shop.'

Everyone should avoid all physical activity outdoors when the air quality index reaches 'hazardous,' considered 'emergency conditions,' the Nevada Division of Environmental Protection said on its website.

'People with heart or lung disease, older adults and children should remain indoors and keep activity levels low.'

Renown Regional Medical Center in Reno has experienced a 'slight increase' in emergency room visits as a result of the smoke, said Jennifer Allen, the hospital's clinical nursing supervisor.

'Patients are experiencing shortness of breath, eye and throat irritation, cough and headache due to the heavy smoke and poor air quality,' she said, adding that people with asthma and other respiratory ailments were most affected.

The pollution levels are among the worst ever recorded for small particulates around Carson City in the state's air monitoring records dating to 2000, according to JoAnn Kittrell, public information manager for Nevada Division of Environmental Protection.

Ash covering a burned out pickup truck is seen in Yosemite National Park on August 28th

Map of the western U.S. highlighting wildfires still being fought by the U.S. Forest Service

The air quality briefly moved into the 'hazardous' level in some areas on Friday as well, she said.

'It's very unusual,' she said. 'We just happen to be in the direct path of the plume from Yosemite.'

The previous peak reading in Reno came on Friday when the air quality index closed in on the 'very unhealthy' stage.

Schoolchildren were kept indoors during recess, high school football practices and scrimmages were canceled through the weekend and an annual air show at Lake Tahoe was canceled due to low visibility.

Carol Chaplin, executive director Lake Tahoe Visitors Authority, said some hotels and motels reported cancellations earlier in the week, but so far there hasn't been any major impact for the upcoming Labor Day weekend.

'I could lie and say it's not affecting anything, but it is,' she said. She said visibility in the scenic Tahoe Basin ebbs and flows with the shifting winds.

This NASA Earth Observatory image obtained August 27, 2013 shows what the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite tracked on the growth of the Rim Fire August 26

'I still see people out on the lake,' she said. 'At least we're not on fire.'

The fire caused air pollution problems in California cities far away from the fire, including those in the Sacramento region.

Two dozen competitors in the 25th annual Best in the West Nugget Rib Cook-Off were taking it in stride as they prepped their grills for the barbeque festival running Wednesday through Labor Day in Sparks, Nev.

The air around the event is usually filled with smoke, albeit a different kind when the barbeque festival's in town.

'You can't have too much smoke at a barbeque,' said Mike Peters of Springfield, Mo., a member of the Kansas City Barbeque Society's Great American Barbeque Tour Team.